Interpretive Summary: Huanglongbing (HLB) or yellow shoot disease (also called greening disease) is highly destructive to citrus production worldwide. The disease was recently found in Florida in 2005. Studies on HLB are very challenging because of limited information about the causal agent(s). Several bacteria have been found in symptomatic tissues of HLB affected trees and even cited as pathogens. We state that without a pathogenicity test, a bacterium should not be called a pathogen, but a disease-associated bacterium. A precise description of HLB related bacteria could have a significant impact on HLB research and formulation of control strategies.

Technical Abstract:
Huanglongbing (HLB) or yellow shoot disease is a destructive disease that threatens citrus production worldwide. The emergence of HLB in Sao Paulo, State of Brazil in 2004 and in Florida of the U.S. in 2005 has increased concern in the citrus production community in the USA. Intensive research is currently underway or being planned to manage the disease. Scientific research publications on HLB are increasing. Commonly, “Candidatus Liberibacter spp.” namely, “Ca. Liberibacter asiaticus”, “Ca. Liberibacter africanus”, and “Ca. Liberibacter americanus”, are referred as the pathogens, i.e. the etiological agents, of HLB. We suggest, however, that a “Ca. Liberibacter. sp.” should not be cited as a pathogen, i.e. the etiological agent, of HLB, because of the non-culturable status of these bacteria and the lack of complete fulfillment of Koch’s postulates. Instead, a “Ca. Liberibacter sp.” should only be referred to as a bacterium associated with HLB.